HD6413007F20 Datasheet, PDF (165/798 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Series

6. Bus Controller
8-Bit Access Areas: Figure 6.5 illustrates data alignment control for 8-bit access space. With 8-bit
access space, the upper data bus (D₁₅ to D₈) is always used for accesses. The amount of data that
can be accessed at one time is one byte: a word access is performed as two byte accesses, and a
longword access, as four byte accesses.
Byte size
Upper data bus
Lower data bus
D₁₅
D₈ D₇
D₀
Word size
1st bus cycle
2nd bus cycle
Longword size
1st bus cycle
2nd bus cycle
3rd bus cycle
4th bus cycle
Figure 6.5 Access Sizes and Data Alignment Control (8-Bit Access Area)
16-Bit Access Areas: Figure 6.6 illustrates data alignment control for 16-bit access areas. With
16-bit access areas, the upper data bus (D₁₅ to D₈) and lower data bus (D₇ to D₀) are used for
accesses. The amount of data that can be accessed at one time is one byte or one word, and a
longword access is executed as two word accesses.
In byte access, whether the upper or lower data bus is used is determined by whether the address is
even or odd. The upper data bus is used for an even address, and the lower data bus for an odd
address.
Byte size
Byte size
· Even address
· Odd address
Upper data bus
Lower data bus
D₁₅
D₈ D₇
D₀
Word size
Longword size
1st bus cycle
2nd bus cycle
Figure 6.6 Access Sizes and Data Alignment Control (16-Bit Access Area)
Rev.5.00 Sep. 12, 2007 Page 135 of 764
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